1. Field of the Invention
The present invention relates to positive electrode plates for alkaline storage batteries and a method for manufacturing the same, and alkaline storage batteries using the same.
2. Description of Related Art
In recent years, alkaline storage batteries have attracted wide attention as power sources for portable equipment, cellular phones, electric cars or the like. In particular, alkaline storage batteries using nickel hydroxide as an active material for positive electrodes have become a focus of attention because they can serve as a secondary battery with a high energy density and an excellent reliability.
In a nickel positive electrode using nickel hydroxide as the active material, after charge-discharge cycles are repeated, a part of the nickel hydroxide changes to γ-nickel oxyhydroxide (γ-Ni(OOH)). This γ-nickel oxyhydroxide has a larger crystal volume than β-nickel oxyhydroxide (β-Ni(OOH)). Accordingly, repeated charge-discharge cycles bring about swelling of the nickel positive electrode and then an increase in the electrode plate volume, so that more electrolyte is retained in the nickel positive electrode. Consequently, the electrolyte amount retained in a separator decreases. The smaller amount of the electrolyte in the separator causes a problem in that an internal resistance of the battery rises, leading to deterioration of output characteristics. There also has been a problem of shortened cycle life.
In order to solve these problems, the following methods have been suggested: a method of adding cobalt hydroxide to the nickel hydroxide (see JP 50(1975)-132441 A), a method of filling nickel hydroxide in a nickel substrate and then generating Co(OH)2 (see JP 57(1982)-5018 B), and a method of incorporating metal cobalt into a sintered nickel substrate retaining an active material (see JP 54(1979)-1010 B). Further suggested is a positive electrode plate containing a nickel substrate containing cobalt, nickel hydroxide that is forming a solid solution with cobalt and cadmium hydroxide that does not form a solid solution with nickel or cobalt (see JP 6(1994)-13076 A).
The above-mentioned conventional methods aim to inhibit the generation of γ-nickel oxyhydroxide so as to prevent swelling of the positive electrode plate, but their effects have not been sufficient.